Highly friction resistant and durable bearing coatings for crankshafts and large end bearings

ABSTRACT

Slide layer for slide bearing, in particular for crankshafts, connecting-rod bearings or large end bearings, comprised of an alloy with several phases, which form a matrix and a dispersed phase, wherein the dispersed phase exhibits only a low solubility in the metal of the matrix, wherein the metal matrix is formed by a Al alloy and the dispersed phase by a Bi or a high melting Bi alloy, as well as slide bearings coated therewith and processes for producing a slide layer by sputter processes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns highly friction resistant and durable bearing coatings for crankshafts, connecting-rod bearings and large end bearings, slide bearings, as well as a suitable manufacturing process.

2. Related Art of the Invention

The conventional processes for production of the bearings of this generic type involves coating a base material (for example steel or light metal) with a bearing or coating, or to clad the base material with a bearing shell.

With the development of new generations of automobile motors, the requirements placed on the materials used in the drive assemblies steadily increase. For high power motors in commercial vehicles or passenger vehicles, in the future peak pressures of up to and beyond 250 bar are to be realized in the combustion cylinders in order to improve efficiency, power and exhaust gas quality.

The available bearings for the drive assemblies, in particular the bearings for the crankshafts, connecting-rod bearings large end bearings, are no longer capable of meeting the high mechanical and thermal strains resulting therefrom.

While previously frequently Pb-containing alloys based on Cu have been used as materials for the slide bearings, these are today, for reasons of environmental protection, increasingly being replaced with alloys free of Pb.

Frequently the slide bearings have on their surface a slide layer of a comparatively soft material. This is formed for example using Pb alloys or Al—Sn— alloys.

From DE 198 01 074 A1 there is known for example a layer composite material as slide element for bearing shells or bearing bushings, in which the materials from the alloy system Cu/Zn/Al or Cu/Al are employed. The slide layer is applied onto the carrier material using a continuous band cast process, in which the carrier material is preheated to a temperature of 1000° C.

From DE 198 24 308 C1 a slide bearing shell is known with a slide layer applied by electron beam vaporization, which is comprised of a compound material of a matrix phase, preferably of aluminum, and a disperse phase, preferably of Sn, Pb, Bi and/or Sb.

As slide bearings for high technical requirements, there are also known Al/Cu alloys with Sn content in the range of 17 to 35 wt. %.

WO 9100375 describes a bearing, of which the bearing surface is comprised of a base material, in particular Al, and a disperse phase, in particular Sn. The layer is applied by a sputtering process.

The known slide bearings and their slide layers cannot exhibit the required long-term stability in the face of these high demands, particularly the combination of high pressure and high temperature, and in the case of dry rubbing conditions do not exhibit the required safety prior to galling or seizing. Particularly with the high demands placed on modern motors a partial short-time loss of oil cooling on the slide surface is not an infrequent operating condition, so that there is a great need for the ability to run while dry.

SUMMARY OF THE INVENTION

It is thus the task of the invention to provide a bearing coating or slide layer, which exhibits an elevated long time endurance, in particular with respect to elevated pressure and temperature loads, and exhibits a reduced tendency towards galling or seizing.

This task is solved in accordance with the invention by a separate bearing layer upon a metal component, in particular for crankshafts, connecting-rod bearings and large end bearings, comprised of an alloy with several phases, which form a matrix and a dispersed phase, wherein the dispersed phase exhibits only a low solubility in the metal of the matrix, as well as by a process for producing a bearing layer of an alloy with a microstructure of a metal matrix and dispersed metallic phase.

DETAILED DESCRIPTION OF THE INVENTION

The separate bearing layer is comprised of an alloy, with a microstructure of several metal phases, wherein one phase represents a metal matrix and a further phase represents a metallic phase distributed or dispersed therein. The disperse metal phase exhibits only a low solubility in the metal of the metal matrix.

In a preferred embodiment of the invention the metal matrix is formed by an Al alloy and the disperse phase by Bi or a high melting Bi alloy.

By this combination of materials it is achieved, that on the basis of the low solubility of the Bi in the Al on the one hand a very finely distributed disperse phase is formed and on the other hand the thermal stability of the disperse phase, and therewith the total bearing layer, is significantly elevated by the comparatively high melting point of Bi or, as the case may be, its alloy, in comparison to known comparable bearing layers. Due to the insulation by unmixed interstices in the Al/Bi system the tendency of the dispersed distributed Bi to recrystallize under the influence of temperature is reduced.

The melting point of the Bi is 271° C., and therewith is significantly higher than that of Sn employed as alloy component in comparable slide bearings or slide layers with a melting point of 232° C.

Conventionally most bismuth alloys are characterized by a low melting point, which is below that of both the bismuth as well as that of the other alloy elements. Bismuth is thus typically employed as alloy component for reducing the melting point of an alloy. A bismuth alloy comprised of bismuth, lead, indium, tin and cadmium exhibits a melting point of below 50° C. Other alloys with bismuth are for example Wood metal (bismuth 50%, lead, tin and cadmium) with a melting point of 71° C., or Lichtenberg-metal (bismuth respectively 50% with varying components tin and lead).

The inventive alloy of Bi exhibits, in comparison, a substantially higher melting point. Preferably the Bi alloys employed have a melting point above 250° C. These include Bi alloys with Sn or Sb in an amount of 3 to 6 wt. %, for example Bi with 4% Sn (melting point: 360° C.) or Bi with 5% Sb (melting point: 296° C.).

One substantial advantage of the inventive combination of metal matrix formed of an Al alloy and a dispersed phase of Bi, or a high melting Bi alloy, is attributable to the low solubility of the two metal main components Al and Bi. While in a eutectic alloy a melt or flux simultaneously forms two crystalline phases at the eutectic temperature, in a monotectic system the homogenous flux or melt decomposes at a temperature (the monotectic temperature) into a solid plus a liquid flux with a composition significantly different than that of the starting flux. This second melt or flux remains liquid until substantially below this temperature. Monotectic alloys belong to the class of the immiscible alloys, that means, in the molten liquid condition there is a region of the composition in which the involved components are not miscible. If the inventive bearing layer is formed or, as the case may be, separated, at elevated temperatures and is rapidly cooled, then there forms thus a very fine microstructure with defined dispersed phase of Bi or, as the case may be, Bi alloy.

In accordance with the invention the preferred content of Bi in the alloy or, as the case may be, bearing layer, is below 50 wt. %, in particular in the range of 10 to 40 wt. %. It si particularly preferred when the slide layer or, as the case may be, bearing layer, exhibits 10 to 30 wt. % Bi, 0.1 to 5 wt. % Cu with the rest being substantially Al.

Further alloy components could include in particular the element Cu, or Mn. Their content preferably lies below 1 wt. %.

In the formation of the dispersed phase, the particle size of the disperse phase is of significance. On the one hand the particles of the disperse phase must have a sufficient size in order to be able to exercise their mechanical effect in the slide system, and on the other hand, they may not be so large that a non-homogenous material results.

The most preferred particle size of the particles of the disperse phase lies in the range of approximately 50 nm to 1 μm. Preferably the essential component of the Bi or the Bi alloy is so finely distributed that no primary phases can be recognized under a light microscope. Particularly preferred is when these phases are likewise amorphous under X-ray, i.e., not detectable by X-ray diffraction examination.

Depending upon the manufacturing process of the sliding layer, very diverse microstructures can be formed, which are differentiated in particular by the distribution of the Bi within the matrix. Thus in the case of, for example, melt processes, very large Bi or Bi alloy exclusions or segregations are formed and, in comparison, if formed by metal organic chemical vapor deposition, they are comparitively very fine.

The metallic matrix of the slide layer, in a preferred embodiment of the invention, is an Al alloy with copper in an amount of 0.1 to 5, particularly preferably up to 3 wt. %. The content of further low melting alloy components is accordingly kept small.

Preferably the Sn-content and/or the Pb-content of the Al alloy is below 0.1 wt. %.

The slide layer forms, in accordance with the invention, the upper-most metallic layer of a slide bearing. The slide bearing is, as a rule, comprised of multiple material layers.

Preferably the slide bearing is formed by a base piece of steel, a layer of bearing metal, a thin adhesion promoting layer and the inventive slide layer. The base piece could also be a bearing shell, which is inserted in the bearing, or likewise could be formed by the bearing itself, wherein then the bearing metal is applied directly upon the bearing outer surface. Suitable bearing metals include in particular Cu/Ni—, Cu/Sn/Bi alloys or bronzes. The bearing metal layer preferably has a thickness in the range of 0.1 to 0.5 mm. The adhesion promoting layer is preferably comprised of Ni— or a Ni alloy in a thickness in the range of 0.2 to 5 μm.

A further aspect of the invention concerns preferred processes for producing the described slide bearing layer. Suitable processes include metal-organic chemical vapor deposition, in which the material is deposited in the form of atoms or small atom clusters. These include PVD- or CVD-processes.

In the separation or depositing from the gas phase, the material is essentially built up without passing through a molten phase. Thereby the inventive alloy materials can be formed with an exceptionally homogenous microstructure with very fine exclusion zones or precipitates or segregations of dispersed phases.

The particularly preferred processes for producing the slide layer include the sputtering process, frequently referred to as cathodic evaporation. For this, an electrical field is applied in a vacuum chamber between the substrate to be coated (anode) and the target (cathode) of the layer material. Electrons located in this field are accelerated and collide with argon atoms, which were introduced into the sealed vacuum chamber (recipient), and ionizes these. This shock ionization brings about formation of a plasma. Upon collision of the accelerated Ar-ions on the cathode, atoms or atom clusters are released therefrom and separate onto the substrate (workpiece).

Suitable Al/Bi alloys can be employed as sputter target, preferably however multiple sputter targets of various composition are employed, for example, of a bismuth-free Al alloy and of the Bi alloy. The mixing relationship can be adjusted by the size or surface area relationship of the various targets to each other. The different targets are alternatingly employed, so that during the separation atomic tiers or layers of Al alloy and Bi alloy alternate. The thickness of the separated atom tiers, and therewith the homogeneity of the layer, can be adjusted and controlled by the sputter times of the various targets.

The layer thickness of the inventive slide layer lies typically in the range of a few μm up to several 100 μm. Particularly preferred is a layer thickness in the range of 5 to 20 μm.

In a preferred embodiment of the invention the layers are separated/deposited upon an adhesive intermediate layer of Ni or a Ni alloy.

The sputter processes have the advantage that the formation of a molten phase of the separated off components is substantially avoided and the size of the separated off particles lies essentially in the range of atoms and atom clusters. The separated off particles lie mixed on a quasi-atomic plane. 

1. A slide layer for a slide bearing, in particular for crankshafts, connecting-rod bearings and large end bearings, of an alloy with several phases, which form a matrix and a dispersed phase, wherein the dispersed phase exhibits only a small solubility in the metal of the matrix, the matrix metal is an Al alloy, the dispersed phase is Bi or a high melting Bi alloy, and the Bi or the Bi alloy exists so finely distributed or divided, that it is amorphous under X-ray or the primary phases are not recognizable under a light microscope.
 2. The slide layer according to claim 1, wherein the Bi content in the total slide layer is 10 to 40 wt. %.
 3. The slide layer according to one of the preceding claims, wherein the melting point of the Bi alloy is above 250° C.
 4. The slide layer according to one of the preceding claims, wherein the Bi alloy includes Sn or Sb in an amount of 3 to 6 wt. %.
 5. The slide layer according to one of the preceding claims, wherein the Al alloy includes copper in an amount of 0.1 to 5 wt. %.
 6. The slide layer according to one of the preceding claims, wherein the Sn content of the Al alloy lies below 0.1 wt. %.
 7. The slide layer according to one of the preceding claims, wherein the Pb content of the Al alloy lies below 0.1 wt. %.
 8. A slide bearing with a base material of steel, a layer of bearing metal, a thin adhesion promoting layer, and a slide layer of an alloy with several phases, which form a matrix and a dispersed phase, wherein the dispersed phase exhibits only a small solubility in the metal of the matrix, the matrix metal is an Al alloy, the dispersed phase is Bi or a high melting Bi alloy, and the Bi or the Bi alloy exists so finely distributed or divided, that it is amorphous under X-ray or the primary phases are not recognizable under a light microscope.
 9. The slide bearing according to claim 8, wherein the bearing metal is Cu/Ni—, Cu/Sn/Bi alloys or bronzes; the adhesion promoting layer is Ni— or Ni alloys; and the slide layer is an Al alloy with 10-40 wt. % Bi. 